Some engines utilize one or more valves that may be adjusted in response to an operating condition of the vehicle. In one example, an engine may have variable valve timing and/or lift that enables adjustment of valve operation depending on operating conditions. Specifically, engines may use variable cam timing powered by a hydraulic actuator to vary intake and/or exhaust valve timing relative to crank angle to improve engine performance over a broad range of conditions. However, hydraulic pressure may not be available during some conditions, such as at low engine speed and/or high engine temperature. When there is insufficient hydraulic pressure to adjust valve operation these devices may have a spring-biased default position.
The inventors herein have recognized disadvantages with these approaches. In some examples, the spring-biased default position results in the valves being positioned in the default setting, regardless of widely varying starting and/or stopping conditions, resulting in degraded engine operation. While one approach may be to increase the size of the hydraulic pump, this may increase parasitic loss and increase weight of the engine, thereby reducing efficiency.
In another approach, the above issues may be addressed by a system for an internal combustion engine of a vehicle, comprising a hydraulic pump configured to be powered at least partially by a source other than the engine; an adjustable hydraulic engine actuator configured to be adjusted by hydraulic fluid of the pump; a control system configured to adjust said adjustable hydraulic actuator.
In this way, when engine conditions would provide insufficient hydraulic pressure, hydraulic actuation can still be achieved. Thus, the range of engine control may be expanded resulting in improved engine performance and increased efficiency.